Directional control valves of this type are used in internal combustion engines, for example for actuating hydraulic camshaft phasers or switchable cam followers. The directional control valves are composed of an electromagnetic actuating unit and a hydraulic section. At least one inflow port, at least one working port and one tank port are formed on the hydraulic section. Certain ports of the hydraulic section can be selectively connected by means of the electromagnetic actuating unit, and the pressure medium flows can therefore be deflected.
For the use of a directional control valve for controlling a camshaft phaser, the hydraulic valve is normally embodied as a 4/3 proportional directional control valve. Such a proportional valve is disclosed, for example, in DE 100 51 614 A1. In this embodiment, the electromagnetic actuating unit is permanently connected to the valve section. The electromagnetic actuating unit has a first magnet yoke, a coil, a second magnet yoke, an activation element and a connecting element which holds electrical contacts serving to supply power to the coil. The activation element is composed of an armature and a plunger rod which is connected in a functionally locking fashion to the armature.
The hydraulic section is composed of a valve housing and a control piston which is arranged in an axially slidable fashion therein. The valve housing is arranged within a receptacle opening in the first magnet yoke and is connected thereto in a positionally fixed fashion. A plurality of grooves are formed on the outer lateral surface of the valve housing, said grooves opening into the interior of the valve housing and serving as pressure medium ports. In the interior of the valve housing, a control piston is arranged in an axially slidable fashion, wherein the outer diameter of the control piston is adapted to the inner diameter of the valve housing. Furthermore, annular grooves, via which adjacent pressure medium ports can be connected, are formed on the control piston.
The coil and the first and second magnet yoke are arranged coaxially with respect to one another. The first and second magnet yokes are offset with respect to one another in the axial direction here. In the region of the first and second magnet yokes there is a pot-shaped armature guiding sleeve located radially within the magnet yokes, in which armature guiding sleeve the armature is held in an axially slidable fashion. The cylindrical inner lateral surface of the armature guiding sleeve serves to guide the armature; the base thereof limits the sliding of the armature in an axial direction.
A closed off space is formed between the base of the armature guiding sleeve and the armature which bears flush against the inner lateral surface thereof. The space can, on the one hand, act in an inhibiting fashion on a movement of the armature away from the base by virtue of a partial vacuum which occurs therein. Furthermore, leakage oil which enters into this space can inhibit axial movement of the armature into the base. In order to counteract this undesired effect, the armature is provided with axial drilled holes or axially extending grooves on its lateral surface for permitting pressure equalization between the spaces in front of and behind the armature.
The armature and the first and second magnet yokes form a flow path for a magnetic field which is brought about through energization of the coil. Energization of the coil causes the armature to be forced in the direction of the second magnet yoke, in which case this movement is transmitted onto the control piston by means of the plunger rod which is attached to the armature. Said control piston is then moved in the axial direction counter to a spring which is supported on the valve housing. The plunger rod is permanently connected to the armature. The armature and the plunger rod therefore form an activation element which, through energization of the coil, can be slid in the axial direction and activates the control piston of the hydraulic section, i.e. positions said control piston within the valve housing of the hydraulic section.
A further directional control valve is disclosed in DE 10 2006 031 517 A1. In this embodiment, the hydraulic section is embodied separately from the electromagnetic actuating unit, and is held in a cavity of a camshaft, with the result that during the operation of the internal combustion engine the hydraulic section rotates with the camshaft. The actuating unit is attached in a positionally fixed fashion to a cylinder head cover or cylinder head. The positioning is in turn brought about by an activation element which comprises an armature and a plunger rod which is connected thereto. In this context, the actuating movement of the armature is transmitted to the control piston of the valve section by means of the plunger rod which is pressed into a receptacle in the armature.